Re: [Patch] Slightly improve powerpc floating point handling

[David Edelsohn <dje dot gcc at gmail dot com>]

On Mon, Nov 19, 2012 at 6:25 PM, Michael Meissner
<meissner@linux.vnet.ibm.com> wrote:
> I am working on support for a future processor, and I noticed that when I did
> the power7 work initially in 2009, that I ordered the DF moves so that the VSX
> moves came before traditional floating point moves.
>
> If reload needs to reload a floating point register, it will match first on the
> VSX instructions and generate LXSDX or STXSDX instead of the traditional
> LFD/LFDX and STFD/STFDX instructions.  Because the LXSDX/STXSDX instructions
> are only REG+REG, reload needs to generate the stack offset in a GPR and use
> this.  Note, for normal loads/stores, the register allocator will see if there
> are other options, and eventually match against the traditional floating point
> load and store.  Reload however, seems to stop as soon as it finds an
> appropriate instruction.
>
> The following patch reorders the movdf patterns so that first the traditional
> floating point registers are considered, then the VSX registers, and finally
> the general purpose registers.  I have bootstrapped the compiler with these
> changes, and had no regressions in the testsuite.
>
> I also ran the spec 2006 benchmark suite with/without these patches (using
> subversion id 193503 as the base).  There were no slow downs that were outside
> of the normal range that I consider to be noise level (2%).  The 447.dealII
> benchmark sped up by 14% (456.hmmer and 471.omnetpp sped up by 2%).
>
> Are these patches ok to apply?
>
> 2012-11-19  Michael Meissner  <meissner@linux.vnet.ibm.com>
>
>         * config/rs6000/rs6000.md (movdf_hardfloat32): Reorder move
>         constraints so that the traditional floating point loads, stores,
>         and moves are done first, then the VSX loads, stores, and moves,
>         and finally the GPR loads, stores, and moves so that reload
>         chooses FPRs over GPRs, and uses the traditional load/store
>         instructions which provide an offset.
>         (movdf_hardfloat64): Likewise.

Okay.

Thanks, David